1. Field of the Invention
The present invention relates to a thin film transistor (TFT) including an active layer formed of an oxide semiconductor, a method of manufacturing the TFT, and a method of manufacturing organic light emitting display device including the TFT.
2. Description of the Related Art
Flat panel display devices such as organic light emitting display devices and liquid crystal display devices include at least one thin film transistor (TFT), a capacitor or the like and a pattern including wirings for connecting these elements formed on a substrate for operation thereof. The TFT is formed of an active layer which provides a channel region, a source region, and a drain region, and a gate electrode that is formed above the channel region and is electrically insulated from the active layer via a gate insulating layer.
The active layer of the TFT as described above is typically formed of a semiconductor material such as amorphous silicon or poly-silicon. When the active layer is formed of amorphous silicon, mobility thereof is low, and thus it is difficult to implement a high-speed circuit therein, and when the active layer is formed of poly-silicon, mobility thereof is high but a threshold voltage of the TFT is not uniform, and thus an additional compensation circuit is necessary. Moreover, according to a method of manufacturing a TFT using a low temperature poly-silicon (LTPS), an expensive process such as laser heat treatment is included, and thus the costs for equipment, investment, and management thereof are high, and the method is difficult to apply on a large-sized substrate. Thus, research has recently been conducted into methods and designs of using an oxide semiconductor as an active layer.